Binuclear complexes of nickel

Dru Lynn DeLaet, Purdue University

Abstract

Conproportionation of (Ni$\sp{\rm II}$(CNMe)$\sb4$) (PF$\sb6\rbrack\sb2$, 1, with Ni$\sp{\rm o}$(CNMe)$\sb4$, 2, results in formation of the new binuclear Ni$\sp{\rm I}$ complex (Ni$\sp{\rm I}\sb2$(CNMe)$\sb8$) (PF$\sb6\rbrack\sb2,$ 3. Reaction of this complex with bis(diphenylphosphino)methane (dppm) yields the novel, a symmetrically bridged complex (Ni$\sb2(\mu$-CNMe)(CNMe)$\sb3$(dppm)$\sb2\rbrack$(PF$\sb6\rbrack\sb2\cdot$CH$\sb2$Cl$\sb2,$ 4. The reduction of 4 with sodium amalgam leads to the formation of the complex Ni$\sb2\sp{\rm o}(\mu$-CNMe)(CNMe)$\sb2$(dppm)$\sb2,$ 6. The Ni-Ni separation is 2.572 (1) A consistent with a Ni-Ni bond. The molecular structure of 6 displays unusual cis,cis-bridging diphosphine ligands. The bridging CNMe ligand of the complex is very basic and can be easily protonated by weak acids to form (Ni$\sb 2(\mu$-CNMeH)(CNMe)$\sb2$(dppm)$\sb2\rbrack$(PF$\sb6\rbrack,$ 7. In comparison to complex 6, 7 possesses a shorter Ni-Ni separation of 2.500 (1) A, shorter C-Ni bond distances for the bridging ligand, and longer Ni-C bond lengths for the terminal CNMe groups, interpreted in terms of a greater contribution of an aminocarbyne valence bond description to the bonding of the $\mu$-CNMeH$\sp+$ ligand of complex 7. The binuclear Ni(O) complex, 6, undergoes two one-electron oxidations (E$\sb{1/2}$ = $-0.51$ and $-0.83$ V vs. Ag/AgCl) form the complex, Ni$\sb2(\mu$-CNMe)(CNMe)$\sb2$(dppm)$\sb2\sp{2+}$, 12. The complex exhibits an unusual trans,cis-diphosphine configuration at the Ni centers and contains a semibridging isocyanide. The electrochemical behavior of 12 in the presence of CO$\sb2$ has been examined. Ni$\sb2(\mu$-CNMe)(CNMe)$\sb2$(dppm)$\sb2\sp{2+}$ reacts with CO$\sb2$ by an EC electrochemical mechanism to afford the CO$\sb2$ complex Ni$\sb2(\mu$-CNMeCO$\sb2)$(CNMe)$\sb2$(dppm)$\sb2$, 13. Complex 13 also has been prepared by reaction of 6 with CO$\sb2$(1). Prolonged reaction of 6 with CO$\sb2$(1) leads to complete carbonylation and Ni$\sb2(\mu$-CO)(CO)$\sb2$(dppm)$\sb2$, 14. The results of labeling experiments using $\sp{13}$CO$\sb2$ and 99% $\sp{13}$C-enriched Ni$\sb2(\mu$-$\sp{13}$CNMe)($\sp{13}$CNMe)$\sb2$(dppm)$\sb2$ are interpreted in terms of a reaction pathway involving O-atom transfer from CO$\sb2$ to the carbon atom of the bridging isocyanide of 6 leading to the formation of Ni$\sb2(\mu$-CO)(CO)(CNMe)(dppm)$\sb2$, 15. The reactivity, solvent effects, and substituent effects dominating the photochemistry of complex 6 are rationalized by resonance and molecular orbital models in terms of a metal to ligand charge transfer excited state for neutral $\mu$-isocyanide complexes Ni$\sb2(\mu$-CNR)(CNMe)$\sb2$dppm$\sb2$, and ligand to metal charge transfer excited state for $\mu$-aminocarbyne complexes Ni$\sb2(\mu$-CNMeR)(CNMe)$\sb2$dppm$\sb2$.

Degree

Ph.D.

Advisors

Kubiak, Purdue University.

Subject Area

Chemistry

COinS